The present invention relates to a solution for sludge formation and xe2x80x9cpi-linexe2x80x9d artefact, while processing silver halide photographic materials.
From an ecological point of view, there is a continuous pressure on waste reduction in photographic processing.
Combined with customer demands for a more convenient processing, this results in ever decreasing replenishing rates for both developer and fixer. Sludge formation is one of the major problems when attempting to further reduce the replenishing rates and to avoid waste. Otherwise for industrial radiography wherein in a normal processing cycle in an automatic processing machine use is made of film transport over racks, wherein each of said racks is provided with a lot of rollers immersed in the different processing baths, pollution by e.g. dust being carried into the processor by the film to be processed and generation of very small metallic silver particles in the developer, due to the development process, together with the evitable manipulations like arrest in development, start of the circulation of processing and regeneration liquids make the generated solid particles become deposited onto the rollers of the racks. So when a film is introduced into the processor as a first film of a whole series of films, its first contact with the first stained roller releases the deposit from the said roller or disturbs the deposited layer and as a consequence thereof, after one rotation of the said roller the unevenly distributed dirt or stain comes into contact again with the transported film surface so that it may be deposited onto said surface. The artefact described hereinbefore, recurrently repeated, not only at the first roller, but also at the further rollers that are mounted onto the racks is called xe2x80x9cpi-linexe2x80x9d as it is recurrently depicted at a distance corresponding with the circumference of the rollers.
A lot of compounds suitable for use as sludge preventing additives are known for developer compositions as has extensively been illustrated in the patent literature, e.g. in GB-A 2 029 037, U.S. Pat. Nos. 3,628,955; 4,169,733; 4,310,622; 4,371,610; 4,391,900; 4,546,070; 5,240,823; 5,356,761; 5,385,811; 5,518,868 ; 5,641,620; 5,707,793 and 5,840,472 as well as in EP-A""s 0 136 582, 0 223 883, 0 785 467, 0 789 272, 0 851 282, 1 061 413 and 1 061 414. None of the proposed solutions can however be considered as an ultimate solution in order to avoid sludge formation in all applied conditions and even U.S. Pat. No. 5,518,868 although moreover offering a solution for the xe2x80x9cpi-linexe2x80x9d artefact from the side of the silver halide photographic material as well as from the side of processing solutions leaves still room for further improvements.
Same can be concluded from GB-A 1,225,406 wherein sulphonated tannin polymers act as generally known dispersing agents, suggesting to have a stabilizing effect on colloidal silver present in the developer while processing, not acting therein as a silver complexing compound due to the absence of a silver adsorbing group in its polymeric structure.
Hence, there remains a continuous need for additives for processing solutions, thereby preventing formation of sludge and xe2x80x9cpi-linexe2x80x9d. Almost all of the additives known from the patent literature have a low molecular weight as a common property. A lot of these compounds are the result of a combination of a strong silver ion complexing group as e.g. a heteroaromatic thiol and a solubilizing group such as a sulphonate or carboxylate. These compounds are known to prevent, or at least inhibit, the reduction of silver ions in solution, to prevent the deposition of silver nanoclusters in the developer and to inactivate the catalytic activity of those potentially formed silver nanoclusters for further reduction of dissolved silver ions.
Disadvantageous however is their ability to dissolve quite a lot of silver ions from the emulsion during processing, which results in a significant increase in silver ion concentration in the developer. However above a critical concentration of silver ions in the developer those compounds, known from the state-of-the-art as xe2x80x9csludge preventing additivesxe2x80x9d, loose their activity. In order to solve this well-known problem, components known as xe2x80x9cdissolution regulators (inhibitors)xe2x80x9d have been added to the developer as has clearly been illustrated in JP-A""s 59-079244, 59-079250, 59-079251, 60-080839, 04-277739 and 04-333046, in EP-A 0 272 217 and in U.S. Pat. Nos. 5,300,410; 5,364,746; 5,457,011; 5,821,040; 6,238,853 and 6,238,854. Typical examples of those dissolution inhibitors are the small heterocyclic thiols without solubilizing groups. They are very effective in preventing or inhibiting dissolution of silver ions in a developer, but they are negativating the desired sensitometry as their influence on speed and developability of the processed silver halide materials is questionable. As depending on the conditions of the developer during processing both speed and developability of the developed materials is decreased to an unexpectable and almost inadmissable extent, it is extremely difficult to balance the ratio of both the sludge preventing compound and the dissolution inhibitor.
As becomes clear from the problems posed hereinbefore, it remains a stringent object to provide chemical compounds as additives avoiding formation of sludge and xe2x80x9cpi-linexe2x80x9d in developer compositions to a better extent than known until now.
The above-mentioned advantageous effects have been realized by providing an aqueous silver halide photographic processing solution having the specific features set out in claim 1.
Specific features for preferred embodiments of the invention are set forth in the dependent claims, while further advantages and embodiments of the present invention will become apparent from the following description.
It has now unexpectedly been found that selected polymeric compounds are very effective in preventing sludge, without negatively influencing (increasing) the dissolution rate of the silver halide and/or (decreasing) developability or speed of photographic materials, when making use therefrom in their processing cycle.
The selected polymeric compounds preventing sludge formation, particularly suitable for use in processing solutions according to the present invention therefore comprise at least one monomer unit having a silver ion completing moiety and at least one monomer unit having a solubilizing group. The group complexing silver ions and the solubilizing group are, in a particular embodiment, comprised in the same monomer unit. In a preferred embodiment according to the present invention the processing solution comprises as an additive a polymeric compound having a thiol or a salt thereof as a group complexing silver ions, a group capable of generating a thiol by hydrolysis or a disulfide. By providing such polymeric compounds having a specific silver affinity reduction of silver ions becomes suppressed or inhibited, and, if colloidal silver would be generated, to stabilize the said silver in dispersed form, further thereby passivating the silver nuclei in order to avoid growth thereof and deposit of mud.
In a further preferred embodiment, the solubilizing group is selected from the group consisting of a carboxylic acid or salt thereof, a sulfonic acid or salt thereof, a phosphonic acid or salt thereof, a phosphate and a sulfate. Moreover it has been shown that non-ionic groups like in (meth)acrylamides and hydrofunctional polymers are very useful additives.
Polymeric compounds suitable for use as xe2x80x9canti-sludgingxe2x80x9d additives in the processing solution according to the present invention can be prepared according to any known polymerisation technique, such as radical polymerisation of ethylenically unsatured monomers, polycondensates for the preparations of e.g. polyesters, polyurethanes and polycarbonates and polymers obtained by anionic or cationic ringopening polymerisations.
Also modifications (polymer analogue reactions) have been shown to offer interesting perspectives in order to reach the objects of the present invention: so e.g. polyvinyl alcohol, polyasparic acid, and polyacrylic acid (without however being limited thereto) can be functionalized with Ag-complexing groups.
In a preferred embodiment the polymeric compound comprises at least one ethylenically unsatured monomer according to formula I. 
wherein:
R1 is selected from the group consisting a hydrogen, a substituted or unsubstituted alkyl group, a substituted or unsubstituted aryl group or a substituted or unsubstituted heteroaryl group
L is a divalent linking group
A is selected from the group consisting of a hydrogen, a metallic or organic counterion or a group capable of generating a thiol upon hydrolysis.
In a most preferred embodiment the ethylenically unsatured monomer according to the formula I is selected from the group consisting of acrylates, methacrylates, acrylamides, methacrylamides, vinylethers and styrenes.
Typical examples of monomers according to the formula I are given in the formulae I-1 to I-15 hereinafter, without however being limited thereto. 
In a further preferred embodiment, the polymeric compound comprises at least one ethylenically unsatured monomer according to formula II: 
wherein:
R2 is selected from the group consisting of a hydrogen, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkylene group, a substituted or unsubstituted aryl group, a substituted or unsubstituted heteroaryl group, a carboxylic acid or salt thereof, a carboxamide, an ester of a carboxylic acid, a ketone or an aldehyde;
L represents a divalent linking group
R3 is selected from the group consisting of a hydrogen, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkylene group, a substituted or unsubstituted aryl group, a substituted or unsubstituted heteroaryl group, COxe2x80x94R5;
R4 is selected from the group consisting of a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkylene is group, a substituted or unsubstituted aryl group, a substituted or unsubstituted heteroaryl group, OR6, SR7, NR8R9 
R5 is selected from the group consisting of a hydrogen, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkylene group, a substituted or unsubstituted aryl group, a substituted or unsubstituted heteroaryl group, OR6, SR7, NR8R9 
R6 and R7 are each independently selected from the group consisting of a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkylene group, a substituted or unsubstituted aryl group, a substituted or unsubstituted heteroaryl group
R8 and R9 are each independently selected from the group consisting of a hydrogen, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkylene group, a substituted or unsubstituted aryl group, a substituted or unsubstituted heteroaryl group; and wherein further
R8 and R9 may be combined to form a ring and
R3 and R4 may be combined to form a ring.
Typical examples of monomers according to formula II are given in the formulae II-1 to II-10 hereinafter, without however being limited thereto. 
The monomers according to the general formulae I and II are preferably copolymerized with a monomer comprising at least one solubilizing group, wherein said solubilizing group is more preferably selected from the group consisting of a carboxylic acid or salt thereof, a sulfonic acid or salt thereof, a phosphonic acid or salt thereof, a phosphate or a sulfate in order to provide a polymeric compound suitable for use as an additive in the processing solution according to the present invention.
Typical monomers having a solubilizing group are acrylic acid, is methacrylic acid, styrene-4-sulfonic acid, 4-carboxymethyl-styrene, itaconic acid maleic acid, fumaric acid, 2-acrylamino-2-methylpro-pane-sulfonic acid, without however being limited thereto.
Typical examples of very suitable polymeric compounds preventing sludge formation, when added to processing solutions according to the present invention are given below, again without however being limitative: 
Copolymer-III.1 of acrylic acid with monomer-I.1
Copolymer-III.2 of styrene sulphonic acid with monomer-I.1
Copolymer-III.3 of acrylamide with monomer-I.1
Copolymer-III.4 of acrylic acid with monomer-I.15
Copolymer-III.5 of styrene sulphonic acid with monomer-I.15
Copolymer-III.6 of acrylic acid with monomer-II.1
Copolymer-III.7 of styrene sulphonic acid with monomer-II.1
Copolymer-III.8 of acrylamide acid with monomer-II.1
Copolymer-III.9 of acrylic acid with monomer-II.2
Copolymer-III-10 of acrylamide with monomer-II.2
According to the present invention the molar ratio of the monomer unit comprising a moiety having silver ion complexing ability to the monomer comprising a solubilizing group is preferably between 1 to 100 and 100 to 1, more preferably between 1 to 100 and 1 to 1 and still more preferably between 1 to 25 and 5 to 1.
The polymeric compound preventing sludge formation may further comprise other monomers besides the monomer unit comprising a silver ion complexing moiety and the monomer unit comprising a solubilizing group.
It is not very significant to discuss the ranges of the preferred molecular weight wherein the sludge preventing polymeric compound is situated: the range between relatively low molecular weights of about 1,000 and high molecular weights of about 500,000 should be considered, but methods for determining those molecular weights are prone to discussion as most of them are relative methods, offering no unambiguous standard. Moreover interactions of the polymeric chain with the experimental environment further lays burden thereupon and may lead to false interpretations of xe2x80x9cmolecular weightsxe2x80x9d.
In a preferred embodiment according to the present invention the processing solution is a photographic developing solution.
Use of a processing solution according to the present invention as described in preferred embodiments in detail hereinbefore is further claimed.
It is further not excluded to make use of the polymeric compound as a coating agent in the protective antistress layers of silver halide materials to be processed. As silver halide photographic materials especially envisaged within the context of non-destructive testing applications reference is made to the materials having been coated with cubic silver halide grains as described in EP-A""s 0 538 947, 0 622 668, 0 620 483, 0 620 484, 0 621 506, 0 698 817, 0 754 971 and 0 754 972 and with tabular silver halide grains as disclosed in EP-A""s 0 678 772, 0 890 875, 1 195 642 and 1 197 797. The halide composition of the cubic or tabular silver halide grains coated in the radiation sensitive emulsion layers is not restricted to grains rich in silver bromide, like the silver bromoiodide grains normally used, but is also related with grains rich in silver chloride.